Methods, Processes, and Compositions for Treating Pulp

ABSTRACT

Methods, processes, and compositions for improving sizing efficiency in a paper-making process are provided. Pulp slurry is treated by using alkenyl succinic anhydride that is emulsified with a polymer emulsifier. The emulsified alkeny succinic anhydride is used in conjunction with paper-making filler particles that are modified with hydroxyl-containing hydrocarbon natural polymer polysaccharide.

TECHNICAL FIELD

The present disclosure relates to a method for improving sizing efficiency of an ASA sizing agent in a paper-making process. In particular, the invention relates to a method for improving the sizing efficiency of a polymer emulsifier emulsified ASA emulsion by treating paper-making filler particles with a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound in the sizing process of paper-making.

BACKGROUND OF THE INVENTION

Paper is a cellulose-containing fiber composite having a typical polar, strongly hydrophilic character, which is to say it can be easily wetted and swelled by aqueous system. When writing on and imprinting paper, and also when processing paper, this results in excessive and uncontrolled penetration of water and other liquids (such as ink, printing inks) into the fibrous web. The resulting problems include weakening of the internal fiber bonding strength, worsening of the mechanical properties, decrease in the dimensional stability, and very poor writing and imprinting ability.

In order to control the wetting and penetration behavior so called sizing agents are employed, which through partial hydrophobization counteract the aforementioned behavior. These auxiliary agents can be added both to the aqueous cellulose pulp (internal sizing) or be applied by way of a surface treatment of the previously formed paper web using an appropriate application system such as a size press, film press, coater and the like (surface sizing). Both methods are employed together for some types of paper.

In a neutral or slightly alkaline paper-making process, neutral sizing agents, such as typical neutral sizing agents including, e.g., alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA) are used. In recent years, the use of neutral sizing agents for the sizing of paper and board has become common throughout the globe. Generally, the neutral sizing agent itself is a water insoluble oil. Therefore, it must be in an emulsion state before addition to the furnish for internal sizing. To get a stable emulsion of the neutral sizing agent, an appropriate emulsifier is of paramount importance. Cationic starch and synthetic acrylamide based polymers are normally used as emulsifiers. Compared to cationic starch, polymer emulsifiers are attracting more attention due to the fact that a large amount of cationic starch has to be used to achieve target sizing efficiency, whereas a relatively much smaller amount of synthetic polymer can be used to obtain a similar effect. Moreover, the use of a large amount of cationic starch greatly increases the chemical oxygen demand (COD) level in the water released from a paper mill, which might cause serious environmental pollution. From environmental protection point of view, it is desirable to replace cationic starch with cationic polymers.

In another aspect, due to cost reduction requirements, more and more fillers, such as CaCO₃, TiO₂ are being added to paper to decrease fiber consumption. However, such typically used fillers detrimentally affect the sizing of alkaline paper. With increasing ash content, that is, more fillers added, the neutral sizing is negatively impacted. More specifically, the effect of the neutral sizing when using polymeric emulsifiers is not ideal compared to cationic starch emulsifiers.

It has been reported in some literature that the sizing efficiency can be improved by surface treating the fillers, mainly focusing on hydrophobization modification and treatment techniques of fillers. U.S. Pat. No. 5,411,639 discloses that a starch/fatty acid soap complex can be obtained by cooking the starch and then mixing the aqueous solution of the starch and the fatty acid soap (sodium or potassium salt of fatty acid) in certain conditions. When such complex is used to modify the filler, the sizing efficiency of the AKD can be effectively improved. U.S. Pat. No. 5,527,430 also discloses a method for improving ASA sizing efficiency wherein a polymer is used to surface modify the fillers so that the surface of the filler become hydrophobic. In both of the two methods, a fatty acid or a salt of the fatty acid is used, and the starch/fatty acid complex is used in a large amount, which causes a complex process. The use of large amounts of chemicals for surface modifying calcium carbonate is not economically suitable for practical applications.

SUMMARY OF THE INVENTION

In view of the above defects in the prior art, the present invention solves the problems by providing a method for improving sizing efficiency of a polymer emulsifier emulsified ASA emulsion, which can significantly improve the efficiency of the neutral sizing.

It has been found that the sizing efficiency of the polymer emulsifier emulsified ASA emulsion can be significantly improved by the use of a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound modified paper-making filler particles as paper making fillers. Moreover, it has been surprisingly found that the above effect can be achieved by modifying an paper-making filler particles with only very small amount of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound.

That is, the invention provides a method for improving sizing efficiency of a polymer emulsifier emulsified ASA emulsion in a paper-making process, comprising: sizing a pulp slurry by using a polymer emulsifier emulsified ASA emulsion as a sizing agent, and, adding, as a paper-making filler, paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound into the pulp slurry.

Furthermore, the invention provides a process for paper-making comprising the steps of: adding paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide into a pulp slurry, at the same time of or before or after adding a polymer emulsifier emulsified ASA emulsion into the pulp slurry.

According to the invention, the sizing efficiency of the ASA sizing can be significantly improved when a polymer emulsifier is used as an emulsifier. According to the invention, the sizing efficiency of the synthetic polymer-emulsified ASA emulsion is not less than the sizing efficiency of the ASA emulsion that is emulsified by a cooked cationic starch emulsifier.

DETAILED DESCRIPTION OF THE INVENTION

If it is not indicated otherwise, the scientific and technical terminology in the specification has meanings the same as understood by one of skill in the art. If inconsistency occurs, the meanings used in the specification should prevail.

The invention provides a method for improving sizing efficiency of a polymer emulsifier emulsified ASA emulsion in a paper-making process, comprising:

sizing a pulp slurry by using the polymer emulsifier emulsified ASA emulsion as a sizing agent, and

adding paper-making filler particles which are modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound as a paper-making filler into the pulp slurry.

ASA

In the context, ASA refers to alkenyl succinic anhydrides, which are known as neutral sizing agent (see, e.g., U.S. Pat. No. 3,102,064). ASA sizing agents are commercially available, such as N7540, N7542, and N7543 from Nalco Co., AS2300 from Kemi Co., etc. ASA is a water soluble oil, and its mixture with water is present in an emulsion. To get a stable ASA emulsion, an emulsifier must be used.

Polymer Emulsifier

As an emulsifier for emulsifying ASA emulsion, cationic starch and acrylamide-based synthetic polymer can be mentioned. In the context, polymer emulsifiers can be a water-soluble acrylamide compound, which can be selected from a group consisting of a copolymer of acrylamide and a cationic monomer as well as a copolymer of glyoxal cross-linked acrylamide and a cationic monomer.

Herein, the cationic monomer can be selected from a group consisting of dimethyldiallylammonium chloride, methylacrolyloxyethyltrimethyl ammonium chloride, N,N,N-trimethyl-3-(2-methylallylamido)-1-propylammonium chloride, N,N′-dimethylamino ethyl methacrylate, quatemary ammonium salt cation of N,N′-dimethylamino ethyl methacrylate, dimethylamino ethyl acrylate, quatemary ammonium salt of dimethylamino ethyl acrylate, diethylamino ethyl acrylate, and quatemary ammonium salt of diethylamino ethyl acrylate.

For example, the polymer emulsifier can be the copolymer of acrylamide and a cationic monomer having a weight average molecular weight of 10,000 to 1,000,000 Dalton, in which the ratio of the cationic monomer unit to the acrylamide unit is between 1/99 and 20/80, for example, between 2/98 and 18/82, or for example, between 5/95 and 15/85.

In the context, a “cationic monomer unit” refers to the moiety of the polymer that derives from a cationic monomer; a “acrylamide unit” refers to the moiety of the polymer that derives from acrylamide. A “glyoxal unit” refers to the moiety of the polymer that derives from glyoxal.

For example, the polymer emulsifier can be a copolymer of a glyoxal cross-linked acrylamide and a cationic monomer having a weight average molecular weight of 100,000-3,000,000 Dalton, in which the ratio of the acrylamide unit to the cationic monomer unit is between 5/95 and 95/5, the ratio of the glyoxal unit to the acrylamide unit is between 60/40 and 5/95, or for example, between 50/50 and 10/90, or for example, between 45/55 and 10/90.

More particularly, the polymer emulsifier can be selected from a group consisting of a copolymer of methylacrolyloxyethyltrimethyl ammonium chloride and acrylamide as well as glyoxal cross-linked dimethyldiallyl ammonium chloride acrylamide.

N7541 and N63007 From Nalco Co. and Bubond 650 from Buckman Co. are examples of commercially available polymer emulsifiers that can be used.

ASA Emulsion Emulsified by a Polymer Emulsifier

A polymer emulsifier emulsified ASA emulsion is known in the art, for example, by reference to U.S. Pat. Nos. 4,657,946 and 6,491,790. A polymer emulsifier emulsified ASA emulsion can be prepared by, for example, mixing e.g., 0.01-10 parts by weight of a polymer emulsifier and 50-99.9 parts by weight of water, and then adding 0.01-40 parts by weight of ASA, stirring in a high shear condition for 1-2 minutes. Herein, the “high shear condition” means that the ASA is dispersed into the water by a mechanical force so as to form an emulsion. The high shear condition can be achieved by known methods in the art. For example, it can be realized by a homogenizer or a turbo pump. In the polymer emulsifier emulsified ASA emulsion, the content of ASA can be in an amount of 0.01-10 wt %. The emulsified ASA particles can have a particle size of, e.g., 0.1-5 μm, or for example, 0.2-2 μm, or for example, 0.5-1.5 μm.

Paper-Making Filler Particles Modified by a Hydroxyl-Containing Hydrocarbon Natural Polymer Polysaccharide Compound

Paper making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound comprise: a core, which is formed by an individual paper-making filler particle or an aggregate of paper-making filler particles; and a covering layer, which is formed by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound and covers the surface of the core. Paper making filler particles modified by hydroxyl-containing hydrocarbon natural polymer polysaccharides can be composed of only the above core and the above covering layer. A “covering layer formed by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound” is intended to mean that the covering layer contains only the hydroxyl-containing hydrocarbon natural polymer polysaccharides as a modifier for the paper-making filler particles.

The hydroxyl-containing hydrocarbon natural polymer polysaccharide compound refers to polysaccharide macromolecule carbohydrates formed by monosaccharide monomer (C₆H₁₀O₆) via glucosidic bond. The specific examples can be selected from a group consisting of cellulose, cationic cellulose, chitosan, cationic chitosan, guar gum, cationic guar gum, cooked native starch and cooked cationic starch, or any combination thereof. Specifically, the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can also be a combination of any, such as two or three or more, selected from the given examples. For example, it can be the cooked starch in combination with one or two or more selected from cellulose, chitosan, guar gum or their cationic compound. For example, it can be the cooked starch (cooked native starch and/or cooked cationic starch in the specification). For example, it can be the cooked native starch.

“Paper-making filler” or “filler for paper-making” is one class of important raw materials for paper making, which can substitute a large amount of pulp fiber for paper making process. The use of the filler can substantially decrease the cost of paper making, and improve the whiteness, opaqueness, smoothness, glossiness of the final paper, the adaptability of the printing and writing, and/or the size stability, etc. In some conditions, it can also improve the drainage of the paper stock in wet end and decrease the cost of the paper-making. The paper-making filler can be an inorganic filler or organic filler. The inorganic filler can be, for example, selected from kaolin, calcium carbonate, talc, titanium dioxide, aluminum hydroxide, calcium sulfate, and amorphous silicate, or any combination thereof. For example, the inorganic filler can be calcium carbonate in combination with one or two or more selected from kaolin, talc, titanium dioxide, aluminum hydroxide, calcium sulfate, and amorphous silicate. The inorganic filler can be, for example, calcium carbonate. The calcium carbonate can be anionic calcium carbonate, for example, anionic ground calcium carbonate or anionic precipitate calcium carbonate; or cationic calcium carbonate, for example, cationic precipitate calcium carbonate or cationic ground calcium carbonate.

The organic filler can be selected from a group consisting of synthetic polymer filler, starch-based filler, wood powder filler, or any combination thereof. The synthetic polymer filler can be, for example, 1,1-dichloroethylene/acrylonitrile copolymer, urea formaldehyde resin agglomerate filler and starch-based filler. The paper-making filler can be, for example, calcium carbonate in combination with one or two or more selected from a group consisting of kaolin, talc, titanium dioxide, aluminum hydroxide, calcium sulfate, amorphous silicate, polymer-based filler, starch-based filler, and wood powder filler. The paper-making filler can be either surface unmodified or surface modified. The surface modification can be carried out by a conventional surface modifier in the art, such as unmodified starch, cationic starch.

“paper-making filler particles” refers to particles of paper-making filler which are not subject to an surface modification. The paper making filler particles can be primary particle (an individual paper-making filler particle), or secondary particle (aggregate of paper-making filler particles). There is no special limitation on the particle size of the paper-making filler particles, as long as it does not influence its use as paper making filler. The paper-making filler particles can have a particle size of such as 0.1-200 μm, e.g., 2-100 μm, e.g., 10-50 μm.

A “covering layer” refers to a layer that covers the surface of the core. The covering layer and the core can have a weight ratio of e.g., 0.1:100-5:100, e.g., 0.2:100-2:100, or e.g., 0.3:100-1.5:100.

The paper making filler particles modified by hydroxyl-containing hydrocarbon natural polymer polysaccharides can be produced by the following methods. The production method includes:

1. Preparation of a solution or a dispersion of the hydroxyl-containing hydrocarbon natural polymer polysaccharides. The solution or dispersion can be, e.g., aqueous solution or dispersion liquid. There is no special limitation to the content of the hydroxyl-containing hydrocarbon natural polymer polysaccharides the solution or dispersion, and it can be suitably selected according to the practical requirement, which can be 0.1-20 wt %, or e.g., 0.2-10 wt %, or e.g., 0.5-5 wt %.

2. Preparation of a suspension of the paper-making filler particles. The suspension can be an aqueous suspension. There is no special limitation to the content of the paper-making filler particles in the suspension, which can be suitably selected according to the practical requirements. For example, the content of the paper-making filler particles in the suspension can be 1-60 wt %, or e.g., 5-30 wt %, or e.g., 10-20 wt %.

3. Mixing the solution or dispersion of the hydroxyl-containing hydrocarbon natural polymer polysaccharides and the suspension of the paper-making filler particles so that the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound covers the surface of the paper-making filler particles. There is no special limitation to the mixing ratio of the solution or dispersion of the hydroxyl-containing hydrocarbon natural polymer polysaccharides to the suspension of the paper-making filler particles, which can be suitably selected according to the practical requirement. For example, relative to the 100 parts by weight of the paper-making filler particles in the suspension of the paper-making filler particles, the hydroxyl-containing hydrocarbon natural polymer polysaccharides in the solution or dispersion of the hydroxyl-containing hydrocarbon natural polymer polysaccharides can be added in an amount of 0.1-20 parts by weight, or e.g., 0.2-10 parts by weight, or e.g., 0.5-5 parts by weight. During and/or after the mixing, the mixing can be facilitated by, e.g., stirring. The obtained liquid can be used as paper-making filler directly, and the prepared paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can also be separated by means such as filtration and/or centrifugation. The weight ratio of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound and the paper-making filler particles in the prepared paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can be adjusted by adjusting the mixing ratio, mixing duration, stirring conditions, filtration/centrifugation conditions of the solution or dispersion of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound and the suspension of the paper-making filler particles.

The weight ratio of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound to the paper-making filler particles in the paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can be determined, for example, by the following method: the obtained paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound is dried by, e.g., heating to remove the contained medium (e.g., water, organic solvent), and then weighed and indicated as M1; the heat-dried paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound is immersed again with a medium (e.g., water, organic solvent) to swell the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound layer, and then the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound layer is removed by a physical method (for example, polishing with sandpaper), dried again, e.g. by heating the obtained paper-making filler particles to remove the attached medium, and then weighed again, indicated as M2; the weight ratio is M1−M2/M2. For example, when the paper-making filler particles is inflammable inorganic filler such as calcium carbonate, the weight ratio can be determined by the following method: separating the obtained paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound by filtration, such as drying at 120° C., to remove the medium (e.g., water, organic solvent), taking a certain amount of the completely dried paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound, weigh, indicated as M1; heating in the air at 550° C. for 2 hours, weigh again, indicated as M2; the weight ratio is M1-M2/M2.

Paper-Making Process

“Paper-making process” or “process for paper-making” is intended to mean a method of making paper products mainly comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet and drying the sheet.

“Pulp slurry” or “pulp” is intended to mean a product obtained from a pulping process. “Pulping” involves a production process of dissociating the plant fiber raw materials by a chemical method or a mechanical method, or a combination of the both, to form a pulp slurry with an inherent color (unbleached pulp) or further to form a bleached pulp. The pulp can be any of known pulps, including but not limited to, mechanical pulp, chemical pulp, chemical-mechanical pulp, and recycled waste pulp slurry, for example, a pulp containing mechanical pulp and/or recycled fiber.

The pulp is subject to pulping and additive adjustment, producing a fiber suspension which can be used in a hand sheet. Such fiber suspension is called as “paper stock”, so as to be distinguished from the paper slurry which is not subject to the pulping and the additive adjustment.

“Wet paper sheet” refers to a product obtained after the pulp stock passed the headbox, the forming section and the press section to be formed and partially drained, wherein the dryness of the wet paper sheet can be in a range of from 35% to 50%, for example. For the sake of clarity, the product which comes from the forming section but is not subject to drainage in the press section is called as “wet paper web”, which can have a dryness in a range of from 15% to 25%, for example.

“Paper sheet” refers to a product obtained after the wet paper sheet is dried in the dryer section. The dryness of the paper sheet can be in a range of from 92% to 97%, for example.

In one aspect, the invention further provides a method for paper making, comprising the steps of:

(a) providing a pulp slurry;

(b) adding paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound into the pulp slurry, at the same time of or before or after adding a polymer emulsifier emulsified ASA emulsion into the pulp slurry, to obtain a paper stock;

(c) forming the obtained paper stock to obtain a wet paper web;

(d) pressing and draining the wet paper web obtained in the step (c) to obtain a wet paper sheet; and

(e) drying the wet paper sheet obtained in the step (d) to obtain a paper sheet.

1. The treatment before flowing onto the wire comprises:

(1) the preparation of paper stock: a paper slurry can be made into a paper stock, and the preparation of the paper stock comprises pulping and additive adjustment (adding additives such as sizings, fillers, pigments and aids). The paper slurry is first subject to pulping wherein the fiber of the paper slurry undergoes treatments such as necessary cutting, swelling and fine fibrosis, so as to provide the paper with physical properties and mechanical properties required by a certain sort of paper and meeting the requirements of a paper-making machine. In order to render the paper sheet useful for writing and resistant to liquid impregnation, improve the paper color, white and tone, increase the transparency of the paper and increase the printing performance of the paper, etc., the paper slurry can undergo sizing, adding filler and staining. Furthermore, various chemical aids can be added to provide the paper with some special properties (for example, enhancing the dry strength, wet strength and eliminating bubbles). In this stage, a part or all of the paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can be added into the paper slurry as a filler. Independently, at the same time of or before or after this, a part or all of the polymer emulsifier emulsified ASA emulsion can be added into the paper slurry as an sizing agent. As a filler, the paper slurry may be added with only the paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound; and/or, as a sizing agent, the paper slurry may be added with only the polymer emulsifier emulsified ASA emulsion. It is apparent that other fillers and/or sizing agents can be added into the paper slurry as required.

(2) supplying the paper stock to the slurry supply system: the paper stock is supplied into the slurry supply system, undergoes treatments such as storing, screening, purifying, de-slagging, de-sanding, de-gassing, and discharges the metal, nonmetal impurities, fiber bundle, lump and air, etc., so as to avoid the adverse effects on the quality of paper and hinder the paper-making process. The slurry undergoes slurry proportion, dilution, concentration adjustment, dosage and pressure elimination, and then flows into the head box and onto the wire for making paper.

2. The paper-making of paper comprises:

(1) stock flow approaching: the paper stock is delivered to the forming section (wire section) through the headbox. The headbox is useful in dispersing the fiber homogeneously and flowing the slurry onto the wire smoothly. The additives for paper making, such as the dry strength aids for paper, the wet strength aids for paper, can be added in the process of stock flow approaching. In this stage, a part or all of the paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can be added into the paper slurry as a filler. Independently, at the same time of or before or after this, a part or all of the polymer emulsifier emulsified ASA emulsion can be added into the paper slurry as an sizing agent. As a filler, the paper slurry may be added with only the paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound; and/or, as a sizing agent, the paper slurry may be added with only the polymer emulsifier emulsified ASA emulsion. It is apparent that other fillers and/or sizing agents can be added into the paper slurry as required.

(2) forming: in the forming section, the paper stock delivered by the forming section is formed into a wet paper web by draining on the wire. The forming section is also referred to as wire section. The dryness of the wet paper web can be in range of from 15% to 25%, for example.

The step (c) can be carried out by the step (1) or (2), but not limited to this.

(3) pressing and draining: in the pressing section, the wet paper web from the forming section is subject to a mechanical pressing to form a wet paper sheet. The dryness of the wet paper sheet can be in a range of from 35% to 50%, for example.

The step (d) can be carried out by e.g., the step (3), but not limited to this.

(4) drying: in the dryer section, the wet paper sheet from the pressing section is dried with a dry cylinder to form a paper sheet. The dryness of the paper sheet can be in a range of from 92% to 97%, for example.

The step (e) can be carried out by e.g., the step (4), but not limited to this.

The amount of the paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound added into the paper slurry can be suitably selected by one skilled in the art according to the requirements, for example, can be 20-30 wt % of the final paper (when the particles are added in several stages, the amount thereof refers to the total amounts). For example, relative to 100 parts by weight of over-dried pulp slurry, the total amount of the added paper making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound can be, e.g., 1-50 parts by weight, or e.g., 10-30 parts by weight, or e.g., 15-30 parts by weight, or e.g., 20-30 parts by weight. The sizing in the above two stages is called as internal sizing, and this way of sizing is the way used in the paper making process. The amount of the added ASA emulsion emulsified by a polymer emulsifier can be suitably selected by one skilled in the art according to the requirement, and such selection is a common skill of the skilled artisan (when the emulsion is added in several stages, the amount thereof refers to the total amounts). The ASA emulsion emulsified by a polymer emulsifier can be added, based on ASA, in an amount of, for example, 0.05-0.5 parts by weight, e.g., 0.05-0.1 parts by weight, relative to 100 parts by weight of over-dried pulp slurry.

Moreover, the paper sheet can undergo, as required, finishing procedures such as calendering, winding and cutting, paper-sorting or rewinding, packaging, etc., so as to produce the paper sheet in to a finished paper in the form of flat or roller. Additionally, in order to improve the quality of the paper sheet, surface sizing, coating and online soft calendar or offline supercalendar can be carried out in the dryer section.

In the paper-making process, the paper slurry provided by a paper stock preparation system is generally subject to a slurry supply system (undergoing a treatment before the paper stock flows onto the wire), the headbox and the forming section, the press section, dryer section, etc.

EXAMPLES

The invention is described in more detail by referring to the following Examples and Comparative Examples, but not limited to these Examples.

1. Preparation of the Cooked Starch or Other Hydroxyl-Containing Hydrocarbon Natural Polymer Polysaccharide Compounds

As a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound, starch (either unmodified starch or cationic starch) need to be cooked for use. Starch paste was formed by cooking a certain amount of the starch in water. The concentration of the starch paste was 2 wt %. For other hydroxyl-containing hydrocarbon natural polymer polysaccharide compounds, a solution or dispersion with a concentration of 1 wt % was formulated at room temperature and stored for future use.

2. Preparation of the Hydroxyl-Containing Hydrocarbon Natural Polymerpolysaccharide Compound Modified Paper Making Filler Particles by Covering the Paper-Making Filler Particles with Cooked Starch or Other Hydroxyl-Containing Hydrocarbon Natural Polymer Polysaccharide Compounds

A suspension of calcium carbonate with a certain concentration was placed in a beaker and a certain amount of hydroxyl-containing hydrocarbon natural polymer polysaccharide compounds was added into calcium carbonate particles under stirring for 10 minutes. After the addition of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compounds, the particle size of the calcium carbonate particles increased significantly.

3. Preparation of the ASA Emulsion Emulsified by a Polymer Emulsifier

0.01-10 g of N7541 or N63007 (both are Nalco products) was mixed with 50-99.9 g of water, and then added into 0.01-40 g of ASA and stirred for 1-2 minutes under a high shear condition, affording an ASA emulsion for sizing.

4. Sheeting Procedure in Laboratory Scale and the Water-Resistance Test of Paper

The composition of the fiber slurry: 20% of needle bleached kraft pulp (NBKP), 20% of Leafwood bleached kraft pulp (LBKP), 20% of Bleached chemi-thermomechanical pulp (BCTMP).

A certain amount of fiber slurry was mixed with a corresponding amount of pretreated filler. After mixing for 5 seconds, wet end starch was added followed by the addition of the polymer emulsified ASA emulsion 15 seconds after the mixing of fiber slurry and pretreated filler. Ten seconds after addition of ASA emulsion, the Nalco product N-61067 was added as retention aid and further mixed for 15 seconds. The stirring was stopped and the furnish mixture was transferred to a Rapid Kothen Sheet Former for sheeting. The formulation of the loaded slurry for sheeting was 20-30 parts by weight of polysaccharide compound-treated calcium carbonate filler relative to 100 parts by weight of the loaded slurry. As a control, untreated calcium carbonate filler was used as filler as well and added into the fiber slurry for sheeting. A paper sheet with a diameter of 20 cm was formed after being drained though 100 mesh form line. Afterwards, the paper sheet was dried in vacuum at 96° C. for 8 minutes, and cured overnight at 24° C. in a constant temperature condition.

The water Resistance of the paper sample is tested by a Hercules Sizing Test, (HST). The HST method is an optical method measuring the resistance of paper to permeation of an aqueous penetrant and is a useful general-purpose test for degree of sizing. The penetration time of the test ink in the paper is used to evaluate the water Resistance of the paper. The ink used in the experiment contains 1% of formic acid (see Tappi Official Method 530).

5. Results of Experiments and Data Analysis Example 1

A solution of cationic chitosan (1% concentration) was added into a certain amount of anionic calcium carbonate suspension under stirring and further stirred for about 20 minutes. The average particle size of calcium carbonate was 1.9 μm before treatment, and increased to about 7-10 μm after treated by the cationic chitosan solution. The weight ratio of the cationic chitosan and the calcium carbonate in the particles was determined as about 0.3:100 to 1.5:100. The treated calcium carbonate suspension was added to a pulp slurry and used for the sheet according to the above step 4. The ASA emulsifier used for the sheet was a Nalco product, N7541, having a structure of a copolymer of methylacrolyloxyethyl trimethylammonium chloride and acrylamide containing 10 mol % cationic charge (DMAEM*MCQ (Dimethylammoniumethylmethyacrylated methylchloride quat)/AcAm(acrylamide)). Calcium carbonate accounted for about 27-30% of the weigh of the final paper, that is, in the 100 parts by weight of pulp slurry with filler, about 27-30 parts by weight was calcium carbonate. The dosage of ASA used in the handsheet making process, the amount of cationic chitosan used to treat the CaCO₃ filler, the particle size of the filler before and after treatment, the HST results and the ash content of the final paper sheet are summarized in Table 1.

TABLE 1 Dosage of cationic chitosan CaCO₃ Ash ASA dosage (kg for treating particle size content of ASA/ton slurry) CaCO₃ (kg/ton) (μm) HST (s) sheet (%) 0.5 0 1.9 2.8 28.0 0.5 3 7.3 3.8 28.1 0.5 8 9.5 10.2 28.5 0.5 12 9.0 20.3 27.9 0.5 15 9.8 26.5 28.5 0.7 0 1.9 11.8 27.2 0.7 3 7.3 17.4 27.9 0.7 8 9.5 29.3 28.1 0.7 12 9.0 38.9 27.4 0.7 15 9.8 52 27.8 0.9 0 1.9 36.1 27.9 0.9 3 7.3 57.6 28.8 0.9 8 9.5 131.5 28.3 0.9 12 9.0 144.1 28.4 0.9 15 9.8 177.0 28.2

It can be seen from the above data that the pretreatment of CaCO₃ filler with cationic chitosan helps to improve the sizing efficiency of the polymer emulsified ASA emulsion. For example, in the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.5 kg/ton, the paper sample obtained from sheeting has a HST value of 2.8 s; and the HST value increases to 26.5 s after the filler is treated with cationic chitosan in a dosage of 15 kg/ton. In the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.9 kg/ton, the paper sample obtained from sheeting has a HST value of 36.1 s; and the HST value increases to 177.0 s after the filler is treated with cationic chitosan in a dosage of 15 kg/ton.

Example 2

A solution of guar gum (1% concentration, the cationic substitution degree is 0.04) was added into a certain amount of anionic calcium carbonate suspension under stirring and further stirred for about 20 minutes. The average particle size of calcium carbonate was 1.9 μm before treatment, and increased to about 9-30 μm depending on the dosage of the guar gum. The weight ratio of the cationic chitosan and the calcium carbonate in the particles was determined as about 0.3:100 to 1.5:100. The treated calcium carbonate suspension was added to a pulp slurry and used for the sheet according to the above step 4. The ASA emulsifier used for the sheet was a Nalco product, N7541. Calcium carbonate accounted for about 30% of the weigh of the final paper, that is, in the 100 parts by weight of pulp slurry with filler, about 30 parts by weight was calcium carbonate. The dosage of ASA used in the handsheet making process, the amount of cationic guar gum used to treat the CaCO₃ filler, the particle size of the filler before and after treatment, the HST results and the ash content of the final paper sheet are summarized in Table 2.

TABLE 2 Dosage of guar ASA dosage gum for treating (kg ASA/ton CaCO₃ CaCO₃ particle Ash content slurry) (kg/ton) size (μm) HST (s) of sheet (%) 0.6 0 2.6 4.5 28.0 0.6 3 8.8 11.1 27.8 0.6 8 25.7 32.3 28.5 0.6 12 32.7 32.6 29.1 0.6 15 21.6 32.7 28.1 0.8 0 2.6 12.1 27.6 0.8 3 8.8 31.2 28.1 0.8 8 25.7 81.3 28.6 0.8 12 32.7 80.2 28.7 0.8 15 21.6 87.6 28.3 1.0 0 2.6 15.5 28.4 1.0 3 8.8 45.0 29.1 1.0 8 25.7 122.3 28.2 1.0 12 32.7 136.5 28.1 1.0 15 21.6 141.3 28.6

It can be seen from the above data that the pretreatment of calcium carbonate with cationic guar gum helps to improve the sizing efficiency of the polymer emulsified ASA emulsion. For example, in the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.6 kg/ton, the paper sample obtained from sheeting has a HST value of 4.5 s; and the HST value increases to 32.7 s after the filler is treated with cationic guar gum in a dosage of 15 kg/ton. In the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 1.0 kg/ton, the paper sample obtained from sheeting has a HST value of 15.5 s; and the HST value increases to 143.1 s after the filler is treated with cationic guar gum in a dosage of 15 kg/ton.

Example 3

Cooked cationic starch solution (2% concentration) was added into a certain amount of anionic calcium carbonate suspension under stirring and further stirred for about 20 minutes. The average particle size of calcium carbonate was 1.9 μm before treatment, and increased to about 100 μm after being treated with the starch solution. The weight ratio of the cationic chitosan and the calcium carbonate in the particles was determined as about 0.3:100 to 1.5:100. The treated calcium carbonate suspension was added to a pulp slurry for sheeting. Calcium carbonate accounted for about 30% of the weigh of the final paper, that is, in the 100 parts by weight of pulp slurry with filler, about 30 parts by weight was calcium carbonate. The composition of the fiber pulp slurry was: 20% NBKP+60% LBKP+20% BCTMP, and the basis weight of the paper was 100 g/m². The polymer emulsifier used in the experiment was a Nalco product, N63007. In Table 3, the test data for water resistance are shown.

TABLE 3 Dosage of cooked ASA dosage cationic starch for CaCO₃ (kg ASA/ton treating CaCO₃ particle size Ash content slurry) (kg/ton) (μm) HST (s) of Sheet 0.5 0 1.9 6.2 29.4 0.5 3 102.9 8.2 29.1 0.5 8 107.2 41.8 29.2 0.5 12 102.6 61.7 29.5 0.5 15 105.0 110.2 28.8 0.7 0 1.9 31.2 29.1 0.7 3 102.9 56.3 29.2 0.7 8 107.2 108.9 29.3 0.7 12 102.6 175.7 29.2 0.7 15 105.0 242.8 29.6 0.9 0 1.9 68.3 29.7 0.9 3 102.9 127.6 29.6 0.9 8 107.2 258 29.7 0.9 12 102.6 308.7 29.2 0.9 15 105.0 395.6 29.5

It can be seen from the above data that the pretreatment of CaCO₃ filler with cationic cooked starch helps to improve the sizing efficiency of the polymer emulsified ASA emulsion. For example, in the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.5 kg/ton, the paper sample obtained from sheeting has a HST value of 6.2 s; and the HST value increases to 110.2 s after the filler is treated with cooked cationic starch a dosage of 15 kg/ton. In the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.9 kg/ton, the paper sample obtained from sheeting has a HST value of 68.3 s; and the HST value increases to 395.6 s after the filler is treated with the cooked cationic starch in a dosage of 15 kg/ton.

Example 4

A solution of cooked unmodified starch (2% concentration) was added into a certain amount of anionic calcium carbonate suspension under stirring and further stirred for about 20 minutes. The average particle size of calcium carbonate was 2 μm before treatment, and increased to about 17-50 μm depending on the dosage of the starch in the treatment solution. The weight ratio of the cationic chitosan and the calcium carbonate in the particles was determined as about 0.3:100 to 1.5:100. The treated calcium carbonate suspension was added to a pulp slurry for sheeting. Calcium carbonate accounted for about 28-30% of the weigh of the final paper, that is, in the 100 parts by weight of pulp slurry with filler, about 28-30 parts by weight was calcium carbonate. The composition of the fiber pulp slurry was: 20% NBKP+60% LBKP+20% BCTMP, and the basis weight of the paper was 100 g/m². The polymer emulsifier used in the experiment was a Nalco product, N63007. In Table 4, the test data for water resistance are shown.

TABLE 4 Dosage of cooked Ash ASA dosage unmodified starch CaCO₃ content (kg ASA/ton for treating CaCO₃ particle size of sheet slurry) (kg/ton) (μm) HST (s) (%) 0.5 0 1.9 2.6 29.9 0.5 3 17.3 17.3 30.5 0.5 8 48.1 67.6 29.8 0.5 12 43.7 86.4 29.6 0.5 15 37.8 122.1 29.5 0.7 0 1.9 8.3 30.2 0.7 3 17.3 64.8 28.6 0.7 8 48.1 111.9 28.2 0.7 12 43.7 144.9 29.1 0.7 15 37.8 172.4 27.9 0.9 0 1.9 16.3 30.3 0.9 3 17.3 87.8 28.1 0.9 8 48.1 155.3 27.9 0.9 12 43.7 215.8 28.6 0.9 15 37.8 240.5 27.5

It can be seen from the above data that the pretreatment of calcium carbonate with the cooked unmodified starch helps to improve the sizing efficiency of the polymer emulsified ASA emulsion. For example, in the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.5 kg/ton, the paper sample obtained from sheeting has a HST value of 2.6 s; and the HST value increases to 122.1 s after the filler is treated with cooked cationic starch a dosage of 15 kg/ton. In the case that calcium carbonate is untreated, the filler is added in an amount of about 28-29 wt % and ASA is added in a dosage of 0.9 kg/ton, the paper sample obtained from sheeting has a HST value of 16.3 s; and the HST value increases to 240.5 s after the filler is treated with the cooked cationic starch in a dosage of 15 kg/ton.

Example 5 Compared with the Case Wherein the Starch is Used as Emulsifier

Cationic starch is one of the most commonly used efficient emulsifiers used in the ASA sizing. The purpose of the example is to compare the sizing efficiency of 7541 as emulsifier when the filler is pretreated with cooked starch with the sizing efficiency of cationic starch directly used as emulsifier. In the experiments, the calcium carbonate filler was pretreated with the cooked starch when 7541 was used as emulsifier. The dosage of the cooked unmodified starch used to pretreat the filler was 10 kg cooked starch per ton of the filler. U.S. Pat. No. 5,411,639 discloses that starch and sodium stearylcarboxylate are used to treat calcium carbonate filler so as to improve the sizing efficiency. In the present experiment, the influence of calcium carbonate on ASA sizing efficiency were compared, wherein calcium carbonate is treated by a complex formed by the addition of sodium stearylcarboxylate into the cooked starch. It can be found from the experiment that cooked starch worked more efficiently to improve the polymer emulsified ASA sizing efficiency than cook starch-sodium stearylcarboxylate complex by the filler treatment approach. N7541 worked more efficiently as an emulsifier when the filler was pretreated as compared to cooked starch where the filler was not pretreated.

TABLE 5 Comparison of the ASA sizing efficiency between N7541 as emulsifier when the filler was pretreated with the cooked starch, and cationic starch as emulsifier ASA dosage Emulsifier CaCO₃ Pretreatment (kg/T) HST(s) N7541 10 kg/T 0.5 24.5 Cooked Unmodified Starch N7541 10 kg/T 0.7 59.1 Cooked Unmodified Starch N7541 10 kg/T 0.9 123.3 Cooked Unmodified Starch Cooked Untreated 0.5 4.8 Starch Cooked Untreated 0.7 38.1 Starch Cooked Untreated 0.9 99.1 Starch N7541 Cooked Unmodified Starch + 0.5 6.35 sodium stearylcarboxylate^(a) N7541 Cooked Unmodified Starch + 0.7 19.4 sodium stearylcarboxylate^(a) N7541 Cooked Unmodified Starch + 0.9 45.4 sodium stearylcarboxylate^(a) ^(a)The cooked starch used to pretreat the calcium carbonate filler contains 5 wt % of sodium stearylcarboxylate with a dosage of 10 kg/ton calcium carbonate. The calcium carbonate was added in an amount of 30% based on the weight of the final paper.

Example 6 Influence of CaCO₃ in Different Contents

In the example, the influences of the starch-treated filler in different filler dosages on the sizing efficiency of the polymer emulsifier were compared, wherein the used starch was the cooked non-cationized unmodified starch. The composition of the used fiber pulp slurry was: 20% NBKP+60% LBKP+20% BCTMP, the basis weight of the paper was 100 g/m², and the polymer emulsifier used in the experiment was a Nalco product, N7541.

TABLE 6 Influence of N7541 as emulsifier in different filler dosages on the sizing efficiency of the polymer emulsifier-emulsified ASA emulsion Calcium Carbonate Pretreatment (kg Cooked Dosage of the ASA dosage Unmodified Starch/t added calcium Emulsifier (kg/T) Calcium Carbonate) carbonate (%) HST(s) N7541 0.9 5 10 345.5 N7541 0.9 5 15 284.4 N7541 0.9 5 20 196.1 N7541 0.9 5 30 73.1 N7541 0.9 10 10 365.6 N7541 0.9 10 15 306.3 N7541 0.9 10 20 259.5 N7541 0.9 10 30 114.3 N7541 0.9 15 10 514.3 N7541 0.9 15 15 393.9 N7541 0.9 15 20 319.8 N7541 0.9 15 30 173.2

It can be seen from Table 6 that the sizing efficiency of ASA decreases with the increase of the amount of the added fillers while the sizing efficiency of ASA is improved when the amount of the starch used for treating calcium carbonate is increased. 

1. A method of treating a pulp slurry of a paper-making process, comprising: sizing a pulp slurry by using an alkenyl succinic anhydride emulsified with a polymer emulsifier, and adding paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound to the pulp slurry.
 2. The method of claim 1, wherein the hydroxyl-containing hydrocarbon natural polymer polysaccharide comprises cooked cationic starch, cooked native starch, cellulose, cationic cellulose, chitosan, cationic chitosan, guar gum and cationic guar gum, or a combination thereof.
 3. The method of claim 1, wherein the paper-making filler particles are calcium carbonate particles.
 4. The method of claim 1, wherein the polymer emulsifier comprises a copolymer of acrylamide and a cationic monomer, a copolymer of glyoxal cross-linked acrylamide and a cationic monomer, or a combination thereof.
 5. The method of claim 4, wherein the polymer emulsifier is a copolymer of acrylamide and a cationic monomer having a weight average molecular weight of 10,000 to 1,000,000 Dalton.
 6. The method of claim 4, wherein the polymer emulsifier is a copolymer of a glyoxal cross-linked acrylamide and a cationic monomer having a weight average molecular weight of 100,000 to 3,000,000 Dalton.
 7. The method of claim 4, wherein the cationic monomer comprises dimethyldiallylammonium chloride, methylacrolyloxyethyltrimethyl ammonium chloride, N,N,N-trimethyl-3-(2-methylallylamido)-1-propylammonium chloride, N,N′-dimethylamino ethyl methacrylate, quatemary ammonium salt cation of N,N′-dimethylamino ethyl methacrylate, dimethylamino ethyl acrylate, quatemary ammonium salt of dimethylamino ethyl acrylate, diethylamino ethyl acrylate, or quatemary ammonium salt of diethylamino ethyl acrylate.
 8. The method of claim 4, wherein the polymer emulsifier comprises glyoxal cross-linked dimethyldiallylammonium chloride acrylamide, a copolymer of methylacrolyloxyethyltrimethylammonium chloride and acrylamide, or a combination thereof.
 9. The method of claim 1, wherein the weight ratio of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound to the paper-making filler particles in the paper-making filler particles modified by the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound is from 0.1:100 to 5:100.
 10. A process for paper-making comprising: combining paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound, an alkenyl succinic anhydride emulsified with a polymer emulsifier, and pulp slurry to obtain a paper stock; forming the paper stock to obtain a wet paper web; pressing and draining the wet paper web to obtain a wet paper sheet; and drying the wet paper sheet to obtain a paper sheet.
 11. The process of claim 10, wherein the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound comprises cooked cationic starch, cooked native starch, cellulose, cationic cellulose, chitosan, cationic chitosan, guar gum and cationic guar gum, or a combination thereof.
 12. The process of claim 10, wherein the paper-making filler particles are calcium carbonate particles.
 13. The process of claim 10, wherein the polymer emulsifier comprises a copolymer of acrylamide and a cationic monomer, a copolymer of glyoxal cross-linked acrylamide and a cationic monomer, or a combination thereof.
 14. The process of claim 13, wherein the polymer emulsifier is a copolymer of acrylamide and a cationic monomer having a weight average molecular weight of 10000 to 1000000 Dalton.
 15. The process of claim 13, wherein the polymer emulsifier is a copolymer of glyoxal cross-linked acrylamide and a cationic monomer having a weight average molecular weight of 100,000-3,000,000 Dalton.
 16. The process of claim 13, wherein the cationic monomer comprises dimethyldiallylammonium chloride, methylacrolyloxyethyltrimethyl ammonium chloride, N,N,N-trimethyl-3-(2-methylallylamido)-1-propylammonium chloride, N,N′-dimethylamino ethyl methacrylate, quatemary ammonium salt cation of N,N′-dimethylamino ethyl methacrylate, dimethylamino ethyl acrylate, quatemary ammonium salt of dimethylamino ethyl acrylate, diethylamino ethyl acrylate, or quatemary ammonium salt of diethylamino ethyl acrylate.
 17. The process of claim 13, wherein the polymer emulsifier comprises glyoxal cross-linked dimethyldiallylammonium chloride acrylamide, a copolymer of methylacrolyloxyethyltrimethylammonium chloride and acrylamide, or a combination thereof.
 18. The process of claim 10, wherein the weight ratio of the hydroxyl-containing hydrocarbon natural polymer polysaccharide compound to the paper-making filler particles in the paper-making filler particles modified by a hydroxyl-containing hydrocarbon natural polymer polysaccharide compound is from 0.1:100 to 5:100. 19-20. (canceled)
 21. A modified paper-making filler particle comprising: a core formed by an individual paper-making filler particle or an aggregate of paper-making filler particles, the core having an outer surface; and a covering layer comprising hydroxyl-containing hydrocarbon natural polymer polysaccharide, wherein the covering layer substantially covers the outer surface of the core, wherein the weight ratio of the hydroxyl-containing hydrocarbon natural polymer polysaccharide to the modified paper-making filler particle is 0.1:100-5:100.
 22. The modified paper-making filler particle of claim 21, wherein the hydroxyl-containing hydrocarbon natural polymer polysaccharide is selected from cooked cationic starch, cooked native starch, cellulose, cationic cellulose, chitosan, cationic chitosan, guar gum and cationic guar gum, and combinations thereof.
 23. The modified paper-making filler particle of claim 21, wherein the core comprises a calcium carbonate particle.
 24. (canceled) 